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a)A=(a+b-c)+(a-b)-(a-b-c)
=a+b-c+a-b-a+b+c
=(a+a-a)+(b-b+b)-(c-c)
=a+b
b)B=(-a-b+c)+(a+b)
=-a-b+c+a+b
=(-a+a)-(b-b)+c
=0+0+c=c
c)C=-(a+b-c)+(-c)+(-a-b)-(a+b+c)
=-a+b-c-c-a-b-a+b+c
=-(a+a+a)+(b-b+b)-(c+c-c)
=-3a+b-c
d)D=-(-a-b)-(b+c)+(c-a+b)-(b-a-c)
=a+b-a+c+c-a+b-b+a+c
=(a-a+a)-(b-b+b)+(c+c+c)
=a-b+3c
\(a,A=\left(a+b-c\right)+\left(a-b\right)-\left(a-b-c\right)\)
\(=a+b-c+a-b-a+b+c\)
\(=a+b\)
\(b,B=\left(-a-b+c\right)+\left(a+b\right)\)
\(=-a-b+c+a+b\)
\(=c\)
\(c,C=-\left(a+b-c\right)+\left(-c\right)+\left(-a-b\right)-\left(a+b+c\right)\)
\(=-a-b+c-c-a-b-a-b-c\)
\(=-3a-3b-c\)
câu d cũng tương tự nha
Bài 1:
a) 8154-(674+8154)+(-98+674)
=8154-674-8154-98+674
=-98
b) -25-21+25-72+49*25
=-21-72+1225
=1132
c) \(\frac{1}{3\cdot4}+\frac{1}{4\cdot5}+\frac{1}{5\cdot6}+\frac{1}{6\cdot7}+\frac{1}{7\cdot8}+\frac{1}{8\cdot9}+\frac{1}{9\cdot10}\)
\(=\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}+\frac{1}{8}-\frac{1}{9}+\frac{1}{9}-\frac{1}{10}\)
\(=\frac{1}{3}-\frac{1}{10}=\frac{7}{30}\)
Bài 2)
a) \(A=\left(-a+b-c\right)-\left(-a-b-c\right)\)
\(=-a+b-c+a+b+c=2b\)
b) \(B=\left(2a+b\right)-3b+\left(a-3c\right)-\left(3a+2c\right)\)
\(=2a+b-3b+a-3c-3a-2c=-2b-5c\)
1. Tính nhanh
a) 8154 - (674 + 8154) + (-98+674)
= 8154 - 674 - 8154 - 98 + 674
= (8154 - 8154) + (674 - 674) - 98
= 0 + 0 - 98
= -98
b) -25 - 21 + 25 - 72 + 49 . 25
= [(-25) + 25] - 21 - 72 + 49 . 25
= 0 - 21 - 72 + 49 . 25
= (-21 - 72) + (49 . 25)
= -93 + 1225
= 1132
c) \(\frac{1}{3.4}\) + \(\frac{1}{4.5}\) + \(\frac{1}{5.6}\) + \(\frac{1}{6.7}\) + \(\frac{1}{7.8}\) + \(\frac{1}{8.9}\) + \(\frac{1}{9.10}\)
= \(\frac{1}{3}-\frac{1}{4}\) + \(\frac{1}{4}-\frac{1}{5}\) + \(\frac{1}{5}-\frac{1}{6}\) + \(\frac{1}{6}-\frac{1}{7}\) + \(\frac{1}{7}-\frac{1}{8}\) + \(\frac{1}{8}-\frac{1}{9}\)+ \(\frac{1}{9}-\frac{1}{10}\)
= \(\frac{1}{3}-\frac{1}{10}\)
= \(\frac{7}{30}\)
2. Bỏ dấu ngoặc, thu gọn biểu thức
a) A = (-a + b - c) - (-a - b - c)
A = (-a) + b - c + a + b + c
A = (-a + a) + (b + b) + (c - c)
A = 0 + 2b + 0
A = 2b
b) B = (2a + b - 3b) + (a - 3c) - (3a + 2c)
B = 2a + b - 3b + a - 3c - 3a - 2c
B = (2a + a - 3a) + (b - 3b) + (-3c - 2c)
B = a(2 + 1 - 3) + b(1 - 3) + c(-3 - 2)
B = a0 + b . (-2) + c . (-5)
B = 0 + b . (-2) + c . (-5)
B = b . (-2) + c . (-5)
a, A=(a-b)-(a-b+c)
=a-b-a+b-c
=(a-a)+(b-b)-c
= 0 + 0 - c
=-c
b, B=(a+b+c)-(a+b-c)
=a+b+c-a-b+c
=(a-a)+(b-b)+(c+c)
=0+0+2c
=2c
t**k cho mình nha!!
chúc hok tốt!!
a) A= (-a - b + c ) - ( -a - b - c )
= -a - b + c +a + b + c
=( -a + a) +( -b + b ) + ( c + c )
= 2c
Vậy A = 2c
b))
A= ( -a - b + c ) - ( -a - b - c )
= [ -1 - (-1) +(-2) ] - [ -1 - (-1) -(-2)
= ( -1 +1 -2 ) - ( -1 +1 +2 )
= -2 -2
= -4
Vậy a=-1 ; b=-1 ; c=-2 thì A== -4
Theo đầu bài ta có:
\(\left(a+b-c\right)+\left(a-b+c\right)-\left(b+c-a\right)-\left(a-b-c\right)\)
\(=a+b-c+a-b+c-b-c+a-a+b+c\)
\(=\left(a+a+a-a\right)+\left(b-b-b+b\right)+\left(c-c-c+c\right)\)
\(=2a\)
A = ( -a - b + c ) - ( -a - b - c )
= -a - b + c + a + b + c
= 2.c
Tính nhanh :
= 27.(-33-21-46) = 27.(-100) = -2700
Rút gọn :
= -a-b+c+a-b+c-2c = -2b
Tk mk nha